My blue tongue skink wont stop burrowing?

my blue tongue skink paco won't bask under his uvb or heat bulb. all he does in the tank is go underground. im afraid he is going to develop metabolic bone disease if he keeps it up. what should i do? hes on aspen right now...i know blue tongues are burrowers in nature but wont he develop MBD if he doesnt get enough UV? please help me..